Studies of the relationship of structure and function of the Ca2+ pumping ATPase of plasma membranes will be continued. Such Ca2+ pumps exist in the plasma membranes of heart, smooth muscle, kidney, brain, intestinal epithelium and several other cell types. These pumps are involved in control of intracellular Ca2+ levels in cells such as those of smooth muscle and in movement of Ca2+ across cell layers such as the kidney tubule epithelium. Information about the regulation of these pumps may thus give information relevant to hypertension and kidney disease, among other conditions. The pump consists of a single polypeptide chain, Mr = 138,000; it is possible to obtain it pure and in reasonable quantity from human erythrocytes. We propose studies designed to create a map of the primary structure of the enzyme, and to locate the various functions of this enzyme on the map. Studies will also be carried out on the regulation of the enzyme by the lipids of the phosphatidylinositol cycle, by proteolysis, by calmodulin, and by phosphorylation.